Tribocorrosion behavior of boronized Co1.19Cr1.86Fe1.30Mn1.39Ni1.05Al0.17B0.04 high entropy alloy

Boride layers were grown on the surface of a Co1.19Cr1.86Fe1.30Mn1.39Ni1.05Al0.17B0.04 high-entropy alloy (HEA) by boronizing at temperatures of 900, 950 and 1000 degrees C for 4 h using nanosized boronizing powders. Characterizations were carried out by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, nanoindentation tests, surface profilometry and ball-on-disc type wear tests. The tribocorrosion behavior of the boronized HEAs and the untreated alloy were investigated in air and in 5% HCl. Microstructural examinations revealed complex metal boride layers on the surfaces of the boronized HEAs, consisting mainly of Cr2Ni3B6, Fe0.4Mn0.6B, Cr0.4Mn0.6B and CrFeB2 phases. The boride layers were silicide-free, with thickness and hardness values of 31.95-64.36 mu m and 23.49-28.09 GPa, respectively. The boronized HEAs exhibited reduced friction coefficients and low wear losses in both ambient air and 5% HCl compared to the untreated HEA. Due in part to the lubricating and cooling effect of the solution, the untreated HEA and the boronized HEAs showed reduced wear losses in 5% HCl compared to air. In air, the wear mechanism of the boronized HEAs was abrasive wear combined with polishing, while in the as-cast HEA the wear mechanism was abrasive wear accompanied by plastic deformation. In 5% HCl, the wear mechanism of the boronized HEAs was abrasive wear accompanied by oxidation and pitting, while in the as-cast HEA the wear mechanism was abrasive wear combined with pitting.